This proposal is directed at an area of research that has important ramifications for understanding the mechanism of signal transduction in the central nervous system and peripheral nervous system that ultimately leads to neurite outgrowth. An expected outcome of the proposed study is to determine that lead interferes with remodeling of neurites and synapses during development and learning. Once this knowledge is known, development of effective neuroprotective therapies for children exposed to lead can begin. Although the neurotoxicity of lead exposure is well documented, the cellular and molecular mechanisms underlying lead neurotoxicity have not been well defined. The applicants have investigated the effect of lead on nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells and the role in this process of extracellular signal regulated protein kinase (ERK), a key component of NGF-induced differentiation. They found that exposure of cells to lead acetate (0 - 100 uM) resulted in enhanced NGF-induced neurite outgrowth and promoted formation of multiple neurites per cell in NGF-treated cells. The long-range goal of this application is to understand the causes of environmentally induced neurotoxicity. The objective of this proposal, which is the first step toward attaining this long-range goal, is to understand the molecular mechanism by which Pb enhances NGF-induced neurite outgrowth and ERK/MAPK activation. The exact mechanism by which Pb enhances ERK/MAPK activation is not known. The hypothesis of this proposal is that Pb enhances neurotrophin-induced neurite growth by interacting with one or more of the seven signaling components in the ERK/MAPK pathway and causes neurotrophin-induced neurite outgrowth. They will test this central hypothesis and attempt to accomplish the overall objective of this application by pursuing the following specific aims: (1) determine the molecular mechanism by which lead enhances NGF-induced ERK activation and neurite outgrowth in PC12 cells. Specifically, they will determine the ability of lead to activate the NGF receptor, I-kA, in the presence of NGF and its effects on downstream proteins Shc, Grb2, Sos, Ras, and Raf and ERK in PC12 cells. (2) Using dominant negative constructs, determine upstream and downstream effectors on ERK/MAPK kinase signaling as described in objective #1. (3) Using cDNA array technology, determine the effects of lead on NGF-induced activation of global gene expression. These aims will be accomplished using inhibitors and dominant negative constructs of the signaling components in the ERK/MAP kinase, SRC kinase, and PI 3-kinase pathway to identify how ERK activation is induced by Pb in PC12 cells.